The physical characteristics of a composite, such as flexibility, strength and glass content, are greatly influenced by the configuration and type of reinforcement. Preferred reinforcement configurations often vary greatly for different molding processes, molding conditions and matrix materials. For example, reinforcements typically used for reinforcing thermoplastic matrix materials may not be compatible with thermosetting molding operations. In thermosetting molding operations, good "wet-through" (penetration of the polymeric matrix material through the mat) and "wet-out" (penetration of the polymeric matrix material through the individual bundles or strands of fibers in the mat) properties are desirable. In contrast, good dispersion properties are of predominant concern in typical thermoplastic molding operations.
For reinforcing a resin matrix material, U.S. Pat. Nos. 3,664,909, 3,713,962 and 3,850,723 disclose fibrous mats of unstranded filaments which can be layered with reinforcing mats of fiber strands.
U.S. Pat. Nos. 4,948,661, 5,011,737, 5,071,608 and 5,098,624 disclose fiber reinforced thermoplastic molded products produced by intimately blending reinforcing glass fibers and thermoplastic fibers into a web and heating the web to the melting point of the thermoplastic fibers while applying pressure to the web to press the web into a consolidated structure.
U.S. Pat. No. 4,112,174 and 4,129,674 disclose a carrier mat useful in the manufacture of roofing materials which includes a web of randomly dispersed monofilament glass fibers, elongated glass fiber bundles and a binder such as urea-formaldehyde for consolidating the mat.
British Patent Application No. 2 104 559 discloses a web, tissue or mat of continuous glass filament yarn entangled with glass fiber monofilaments and coated with a resin bonding agent which is useful for reinforcing plastic moldings.
U.S. Pat. Nos. 5,108,678 and 5,194,462 disclose a fiber reinforced plastic sheet having a gradient layer structure wherein less opened strands are concentrated in the lower layers and more opened strands are concentrated in the upper layers of the structure.
The foregoing references do not adequately address the challenges of thermoset vacuum molding processes, in which there is a long-felt need for a glass fiber reinforcement which is compatible with thermosetting matrix materials and which provides composites having good surface characteristics such as hydrolysis and ultraviolet radiation resistance and physical properties such as stiffness and strength.